Typical Values for External Pull-Up Resistor on a NI USB 6009 Digital Output Line?

[diarmaede]

Hi All,

I am using a digital line on a USB-6009 to control an SSR per the attached diagram (from the USB 6009 user manual).  I don't have access to a decade box or variable resistor, so I am hoping to get a good ballpark estimate for the value of Re.  When I connect the SSR to a 5VDC power supply, it pulls 8.2mADC when closed.

Any suggestions?  Is there any other information I can post to help with the guestimations?

Thanks!

[diarmaede · Accepted solution]

I found an old Heathkit decade box and figured out the correct resistance rating, 100 Ohm.

[johnsold]

Why do you need a pull up resistor to control an SSR?

Connect the SSR control input like the LED and resistor (which is what is inside the SSR) as shown in item 1 of Figure 14 on page21 of the USB-6008/6009 manual. Configure the device for open collector digital output.  It can drive 8.5 mA.

Lynn

[diarmaede]

I tried that first.  It did not work.  I'm not sure why.

[stlchem]

I have same situation and am unsure this is a complete answer. Is the external resistor not going to depend on the resistance of the load and have to be determined for each case?  Also I wonder if someone can explain the circuit. I thought that the setting the output to high pulls the current to that line. Like in the example that johnsold referred to where the current is pulled through the LED from the 5V source. (BTW that does not allow for the full 8.5 mA and is why you need the external pull up resistor according to the Guide). So how does the additional connection to ground generate the additional current only when the line P0 changes state?

Thanks for any help. I am just starting to learn.

[MQI]

Use pull down resistor (10K) and you need to limit voltage into you SSR (100 Ohm).  It should work.